CLEANING THE PLATE.] UNUULATORY FOR CES. LIGHT PHOTOGRAPH Y. 



147 



atmosphere, because another film of air or moisture will 

 speedily form on its surface. 



By such means a glass plate may be thoroughly cleansed 

 from every kind of matter prejudicial to its employment 

 for photographic purposes; presuming, of course, that 

 the chemical nature of the glass is such as to present no 

 other difficulty. We may here mention, that although 

 glass, in a practical point of view, may be considered 

 perfectly insoluble in any agent ordinarily employed to 

 cleanse it such is not strictly true. We are inclined to 

 believe, that solutions of potash, nitric acid, ifec., often 

 employed by photographers to cleanse their glass plates, 

 act in an unexpected manner in producing many of the 

 difficulties which frequently present themselves. We 

 are the more inclined to urge this point on our readers, 

 from having found great difficulty in cleansing glass for 

 the purpose of several experiments on polarised light, 

 introduced in our previous pages. Even the mere 

 mechanical action used in rubbing a piece of good glass, 

 by means of a towel, silk handkerchief, chamois leather, 

 ' <kc. , is quite sufficient to form minute lines, which are 

 worked thus into its surface, and, therefore, render such 

 uneven. Whilst visiting several mills in the north of 

 England and Scotland, we were surprised to find in a large 

 "doubling" establishment that of Messrs. Coats, of 

 Paisley that thick glass rods, -which have been employed 

 as rollers, over which the cotton thread had to pass whilst 

 being wound on the spindles, were cut through, in some 

 places, to the depth of a quarter of an inch, by the soft 

 cotton filaments. The two following experiments will 

 impress this fact on the minds of our readers ; and, at 

 the same time, will show the necessity of great caution in 

 rubbing or cleansing glass surfaces, whether in the form 

 of lenses in the camera, or of plates intended to receive 

 pictures on their surface. 



Experiment 9. Into a perfectly clean test-glass or 

 wine-glass, pour a weak solution of carbonate of potass ; 

 then add a solution of tartaric acid both being made by 

 means of distilled water. Immediately after mixing the 

 liquid, rub the sides of the glass, by means of the smooth 

 end of a glass stirring-rod. After a short time, minute 

 crystals of bitartrate of potass will be deposited only on 

 those places which have been rubbed with the rod. Now, 

 as we know that crystals always require an angular pro- 

 jection to cause them to be deposited on a surface, we 

 may justly conclude that such has been produced on the 

 inside of the glass, although by means seemingly in- 

 adequate to produce the effect. 



Experiment 10. Rub a piece of plate or window-glass 

 repeatedly in the same direction, by means of an appa- 

 rently soft towel. Allow it to cool from the production 

 of heat which the friction will evolve. If the rubbed 

 surface be then breathed on, a series of minute lines may 

 generally be observed on holding the glass at an angle, 

 and by viewing it by the light reflected from its surface. 



We thus observe, that the polished surface of any body, 

 no matter how hard it may appear, is really affected by 

 others of a much softer nature, by rapid or peculiar 

 mechanical action. As an expansion of the illustrations 

 we have offered, we may state, that a piece of soft iron 

 revolving rapidly, will cut a piece of hard steel as readily 

 as a knife would a loaf of bread. We may, therefore, 

 urge on our readers an excellent old saying of the 

 Greeks " hasten slowly" as a motto to be held in mind 

 when they are preparing plates for the camera. 



One of the best tests of the perfect cleanliness of a glass 

 plate, is the even condensation of moisture on every part 

 of its surface. This indicates that its external condition 

 is uniform in every place ; and such is exactly the con- 

 dition which an aspirant to success in the art should at 

 all times endeavour to obtain. 



After the plate is thus prepared, be careful to touch it 

 in no part, except at those edges which are at the extremes 

 of its diagonals. This rule should be observed carefully 

 throughout all the subsequent processes : the only excep- 

 tion allowable, is that in which the plate mus*. be held 

 in certain positions during the time the collodion is 

 poured on its surface a process which we have now to 

 enter upon. 



2. Coating the Plate with Collodion. The next step in 

 our process is that of coating the cleaned plate with 

 collodion. But before describing this, we shall give 

 some directions Vith respect to arranging the camera, 

 and thus of having it ready to receive the plate made 

 sensitive by a subsequent process. The professional 

 photographer generally has an assistant, who cleans the 

 plate whilst the operator is getting the camera ready for 

 it. As, however, we presume that our readers will 

 work alone, we need scarcely state, that the camera 

 should be adjusted before the plate is coated and made 

 sensitive. 



The person whose likeness is to be taken should put 

 himself into a natural position, free from constraint, and 

 in such a posture that all the muscles of the body may 

 be, comparatively speaking, at rest. In our opinion, 

 there is a vast deal more art in sitting to have a portrait 

 taken, than in taking it. Almost every one experiences 

 a degree of nervousness ; and each determines to maintain 

 a strict and grave deportment, which, by its affectation, 

 increases, or at all events disposes to beget, nervous 

 irritability. Hence, most persons complain that their 

 " likenesses" are not like them; nor, indeed, can they 

 be, when individuals practically determine, on such occa- 

 sions, to assume airs and graces which, like ladies' best 

 dresses and drawing-room furniture, are only used on 

 " state occasions. " 



A support of some kind is required to maintain the 

 head in its position ; because the muscles of the neck are 



Kig. 153. 



apt to become fatigued 

 if a long "sitting" be ne- 

 cessary. Contrivances 

 of this kind are of 

 various shapes; two of 

 which are represented 

 in the annexed figure. 

 One of these (Fig. 152), 

 as will be observwl, may 

 be attached to the back 

 of a chair; whilst the 

 other (Fig. 153) stands 

 on its own pedestal It 

 will be found, in practice, 

 that the latter is the 

 most convenient, be- 

 cause it is easily adj listed 

 to any position. The 

 rest for the head is the 

 curved portion at the 

 top of each figure ; and 

 should be so arranged as 

 to support the head of the sitter just behind each ear ; 

 and, of course, out of sight with respect to the camera, 

 or they will be included in the portrait. 



In arranging either of these supports, let them be 

 employed solely as rests to support the head, and to 

 prevent fatigue; and not as a framework, by which a 

 rigidity of position would be induced, and stiffness of 

 carriage promoted. 



Having adjusted the position of the sitter, place the 

 camera in front of him ; and after removing the brass 

 cap from the front of the lens, adjust the camera in such 

 a position, that if you are taking the bust only, its image 

 shall occupy the centre of the ground-glass plate. This 

 is of course done by looking at the image on the ground 

 glass ; by shifting the camera to and fro ; and focussing 

 the lenses until a clear and distinct picture is observed. 



In obtaining a good focal view, pay especial attention 

 to the forehead and face, which of course form the es- 

 sential points of the picture : and, in getting these 

 correctly, the value of your lenses will at once be tested, 

 and your full skill and judgment called into exercise ; on 

 which, in fact, success will depend. These points having 

 been attended to, the ground glass is stUl to be left 

 in the frame, so that the focus may be readjusted 

 just previous to introducing the sensitive plate into 

 its place. 



Although a plate coated with collodion only, is un- 

 acted upon by light, still we shall presume that all tho 



